An endogenous molecular oscillator known as the circadian clock controls important biological processes from daily human sleep/wake cycles to plant leaf movements. A major function of the circadian clock is to precisely coordinate physiological responses of an organism to daily environmental changes. The molecular mechanisms underlying the integration of environmental stimuli and the clock are not well understood in many organisms. My objective is to understand how environmental signals are integrated into the circadian clock and the function of specific genes involved in this integration, using Arabidopsis as a model system. Experiments presented in this proposal are designed to provide insight into the function of Early Flowerings (ELF3), a key regulator that regulates the sensitivity of light into the clock throughout the day, allowing for circadian rhythms to progress in constant light conditions. Similar mechanisms exist in the mammalian clock, although the molecular components involved in the response are unknown. The specific aims of this proposal are to: 1. Characterize interactions between ELF3 and known clock associated proteins in vivo. Biochemical and genetic interactions between specific clock proteins that are co-expressed and interact in vitro will be analyzed. 2. Identify novel proteins that interact with ELF3. Yeast two-hybrid assays and affinity purification techniques coupled with mass spectrometry will be used to identify novel ELF3 interacting proteins. Identified candidates will be analyzed by biochemical and genetic approaches in vivo. Relevance: The circadian clock allows for the proper coordination of daily human behaviors, such as sleep/wake cycles, with the diurnal rising and setting of the Sun. Research to elucidate the complex molecular mechanisms underlying the circadian clock in plants will complement similar analyses in other systems, ultimately leading to a better understanding of the circadian clock in humans, allowing for the treatment of circadian disorders.